A bearing liner is utilized between relatively movable members to provide a low friction, wear resistant surface. Relative movement between the members inherently results in wear of the bearing liner and consequent reduction in its thickness. When the bearing liner has been thinned a predetermined amount, the bearing liner must be replaced.
The wear rate is the amount of wear or thinning of the bearing liner per cycle of movement between the relatively movable members. It is obviously desirable to reduce the wear rate to thereby increase the life of a bearing liner.
Typically, a bearing liner is adhered to a substrate. The substrate is not highly polished and has numerous minute projections. For example, these projections may have a maximum height of the order of .003 inch above the mean surface elevation of the substrate, i.e., the surface elevation of the substrate which has one-half of the substrate surface lying above it and one-half of the substrate surface lying below it. The bearing liner has a wear surface which is adapted to engage and slidably support another member which is movable relative to the substrate. In use, the bearing liner is compressively loaded between the substrate and this member.
Bearing liners of the type to which this invention is directed are thin and deformable. Accordingly, loading of the bearing liner against the substrate causes the projections of the substrate to locally deform the bearing liner and provide protrusions on the wear surface. In other words, under load, the relatively thin bearing liner tends to assume the configuration of the irregular surface of the underlying substrate.
As a consequence, the wear surface becomes irregular and includes numerous protrusions formed by the projections on the substrate. Initially, the member engaging the wear surface is supported substantially entirely by the relatively small area of the protrusions, and this results in very rapid initial wear, i.e., a high wear rate. The high initial wear rate continues until all of the protrusions have been worn off so that the wear surface presents a smooth, regular contour. This high initial wear rate materially reduces bearing liner life.
Common assignee's copending application Ser. No. 436,670 filed concurrently herewith in the name of Alfred J. Capelli and entitled "Bearing and Bearing Liner Having A Compliant Layer" provides one solution to this problem. In application Ser. No. 436,670 referred to above, there is disclosed a bearing liner in which a compliant layer is provided between the substrate and the wear resistant portion of the bearing liner. The compliant layer isolates and protects the wear resistant portion from the irregular surface of the substrate, and accordingly, the tendency of the projections on the substrate to produce protrusions on the wear resistant portion of the bearing liner is substantially reduced or eliminated. By reducing the size and number of the protrusions on the wear resistant portion, the high initial wear rate which conventional bearing liners experience is substantially reduced.